The present invention relates to a structure of a display device that allows users to view virtual images.
Augmented reality (hereinafter, AR) is a technology that overlays image information on a real space. In recent years, the AR technology has been drawing attention in the fields of entertainment and work support system. A means for achieving the AR is a display device that generates a virtual image by reflecting an optically generated image on the user side by using an optical branching element, overlays the virtual image on a real space, and displays the virtual image to the user. In particular, the AR display device installed in the plane or vehicle is referred to as a head up display (hereinafter, HUD). HUD displays speed and the like to reduce the visual line movement of the operator, contributing to safe driving.
The technology of a display device for providing such a virtual image is disclosed in Patent document 1 (Japanese Unexamined Patent Application Publication No. 2004-20605) and Patent document 2 (Japanese Unexamined Patent Application Publication No. 2010-197493).
More specifically, Patent document 1 describes a head up display that provides a virtual image by reflecting a real image on a display unit by a concave mirror, and by reflecting a display light by a windshield. Patent document 1 discloses a technology for downsizing by providing a prism sheet in the optical path from the concave mirror to the windshield.
Further, Patent document 2 discloses a technology that allows virtual images to be visible from different viewpoints, by providing a movement mechanism to adjust the incident angle of an image light projected from the optical unit to the windshield, and a lens optical system to correct the distortion of the image projected on the windshield.